FIG. 1 illustrates a cross section of a traditional coreless PM motor. The coreless PM motor comprises a stator and a rotor. The stator comprises a housing 20′, two end caps 21′ and 23′ that are mounted at respective ends of the housing 20′, and two winding discs 28′ that are fixed to the housing 20′. The rotor comprises a shaft 31′, three permanent magnet discs 32′ that are axially charged and fixed to the shaft 31′, two magnetically conductive discs 34′ that are attached to two of the magnet discs 32′. The magnet discs 32′ and the winding discs 28′ are arranged alternately. As is illustrated by arrows, the magnetic field generated by the magnet discs 32′ forms a closed loop by passing through the winding discs 28′, the magnet discs 32′ and returning back in the magnetically conductive discs 34′. The axial length is increased because of the magnetically conductive discs 34′.
Further more, each of the winding discs 28′, the magnet discs 32′ and the magnetically conductive discs 34′ is a single piece disc. During the production of the motor, the winding discs 28′, the magnet disc 32′ and the magnetically conductive discs 34′ are mounted one by one in the axial direction. It is time-consuming and thus expensive to assemble. Therefore, there is a desire for an improved coreless PM motor which is easier to assemble and has a shorter axial length.